1. Technical Field
The present invention relates to a discharge lamp, a light source device, and a projector.
2. Related Art
Conventionally, projectors are used in a variety of application areas including image projectors for presentations in meetings and home theater systems in homes. Most of the projectors incorporate a light source device such as a discharge lamp having electrodes. For example, the discharge lamp is a halogen lamp, a metal halide lamp, or a high-pressure mercury lamp.
However, in production of the discharge lamp as above, it is known that entry of an alkali metal into an electrical discharge space inhibits electrical discharge or promotes reaction of the metal with tungsten to cause a milky clouding (devitrification) of the arc tube. Additionally, an excessive amount of oxygen in the arc tube also promotes devitrification of the arc tube. In order to solve the above problems, for example, JP-A-1996-287867 discloses a discharge lamp. The discharge lamp uses zirconium and tantalum as a getter material disposed on an electrode portion to allow the getter material to adsorb an impure gas (such as oxygen or hydrogen) generated at high temperature.
In the disclosed discharge lamp, however, the getter material is consumed at one time when the lamp is in its on state. In other words, although the getter material disposed on the electrode portion can eliminate oxygen or the like remaining in the electrical discharge space, oxygen is always supplied in the arc tube made of quartz glass (SiO2) under a high temperature condition during lighting of the lamp even after consumption of the getter material. As a result, oxygen excessively supplied in the electrical discharge space causes devitrification of the arc tube. Thus, for improvement in a life span of the discharge lamp, the amount of oxygen in the electrical discharge space needs to be appropriately adjusted.